database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-10-16 17:07:43 +03:00
Code Activity

Switch to CRC-32C in WAL and other places.

Browse Source 
The old algorithm was found to not be the usual CRC-32 algorithm, used by
Ethernet et al. We were using a non-reflected lookup table with code meant
for a reflected lookup table. That's a strange combination that AFAICS does
not correspond to any bit-wise CRC calculation, which makes it difficult to
reason about its properties. Although it has worked well in practice, seems
safer to use a well-known algorithm.

Since we're changing the algorithm anyway, we might as well choose a
different polynomial. The Castagnoli polynomial has better error-correcting
properties than the traditional CRC-32 polynomial, even if we had
implemented it correctly. Another reason for picking that is that some new
CPUs have hardware support for calculating CRC-32C, but not CRC-32, let
alone our strange variant of it. This patch doesn't add any support for such
hardware, but a future patch could now do that.

The old algorithm is kept around for tsquery and pg_trgm, which use the
values in indexes that need to remain compatible so that pg_upgrade works.
While we're at it, share the old lookup table for CRC-32 calculation
between hstore, ltree and core. They all use the same table, so might as
well.
This commit is contained in:
Heikki Linnakangas
2014-11-04 11:35:15 +02:00
parent 404bc51cde
commit 5028f22f6e
20 changed files with 299 additions and 340 deletions
Download Patch File Download Diff File Expand all files Collapse all files

12
src/backend/utils/adt/tsquery.c
View File

@@ -280,9 +280,9 @@ pushValue(TSQueryParserState state, char *strval, int lenval, int16 weight, bool
errmsg("word is too long in tsquery: \"%s\"",
state->buffer)));
INIT_CRC32(valcrc);
COMP_CRC32(valcrc, strval, lenval);
FIN_CRC32(valcrc);
INIT_LEGACY_CRC32(valcrc);
COMP_LEGACY_CRC32(valcrc, strval, lenval);
FIN_LEGACY_CRC32(valcrc);
pushValue_internal(state, valcrc, state->curop - state->op, lenval, weight, prefix);
/* append the value string to state.op, enlarging buffer if needed first */
@@ -883,9 +883,9 @@ tsqueryrecv(PG_FUNCTION_ARGS)
/* Looks valid. */
INIT_CRC32(valcrc);
COMP_CRC32(valcrc, val, val_len);
FIN_CRC32(valcrc);
INIT_LEGACY_CRC32(valcrc);
COMP_LEGACY_CRC32(valcrc, val, val_len);
FIN_LEGACY_CRC32(valcrc);
item->qoperand.weight = weight;
item->qoperand.prefix = (prefix) ? true : false;